Isoprene butyrate and process for



Patented June 24, 1941 ISOPRENE BUTYRATE AND PROCESS FOR MAKING SAME Frank J. Soday, Upper Darby, Pa., assignor to The United Gas Improvement Company, a corporation of Pennsylvania Application June 2, 1939,

No Drawing.

Serial No. 276,969

12 Claims.

The present invention relates to new compositions of matter and to methods for their preparation.

More particularly, this invention pertains to isoprene butyrates and to methods for the preparation of these isoprene derivatives.

By the term isoprene butyrate throughout the specification and claims is meant a butyric acid ester of isoprene alcohol, which alcohol may alternatively be designated as dimethylvinyl carbinol (see Whitmore, Organic Chemistry (1937), page 56) or as 2-methyl-2-hydroxy butene-3.

This invention is based upon the discovery that isoprene butyrate having the general formula and CHa CH3 Isoprcnc isobutyratc may be prepared in excellent yields through the reaction of the corresponding butyric acids or their salts or derivatives upon isoprene alcohol, isoprene alcohol derivatives, such as the metal derivatives, or hydrohalogen derivatives of isoprene. High yields are obtained despite the fact that tertiary alcohols as a rule either do not react at all with organic carboxylic acids, or react with very low yields.

It is an object of the present invention to provide new compositions of matter, namely, isoprene n-butyrate and isoprene isobutyrate, and a process for the preparation thereof. Another object of this invention is to provide new compounds having utility in a number of chemical and related industries. More specifically, it is an object of this invention to provide isoprene derivatives which may be used as solvents for paints, lacquers, varnishes, enamels or similar coating compositions. Another specific object of this invention is to provide compounds which may be used as ingredients in perfumes and various pharmaceutical preparations. Still another specific object of this invention is to provide 'compounds which may be used as intermediates in chemical synthesis. Other objects and advantages of the invention will be apparent to those skilled in the art from the following description.

Isoprene, having the general formula CH3 H CH2=U-U=CH2 is the basic component in the preparation of these new compositions of matter, namely, isoprene n-butyrate and isoprene isobutyrate. It

may be obtained from various sources, such as synthetically from the pyrogenic decomposition of rubber, or from fractions obtained upon the fractionation of condensates obtained in the manufacture of carburetted water gas, oil gas, refinery gas, or coke oven gas, or from similar sources. Such fractions will be referred to herein, generally, as light oil isoprene fractions. Such fractions obtained in the manufacture of oil gas are particularly preferred.

Hydrocarbon fractions containing from 5 to 100% of isoprene may be successfully used in the production of the herein described isoprene derivatives, although in general the use of fractions containing from to isoprene is preferred for the production of products of high quality.

In general, the initial step in the preparation of my new isoprene derivatives is the conversion of isoprene into a monohydrohalogen derivative.

The preparation of the hydrogen halide derivative may be effected in a number of ways.

For instance, liquid or gaseous hydrogen halide may be introduced'into isoprene, or into an isoprene fraction, say by means of a porous tube, or a pipe containing a porous cap, or otherwise.

0n the other hand, liquid or gaseous hydrogen halide may be contacted with liquid or gaseous isoprene or isoprene fraction in a kettle, or in an open or packed tower, or otherwise.

The reactants may be contacted in any desired manner, for instance, concurrently, or countercurrently, or in a static system.

I prefer to employ hydrogen chloride as the hydrogen halide. However, other hydrogen halides such as hydrogen bromide, hydrogen iodide, or hydrogen fluoride, may be employed without departing from the spirit of the invention.

When a hydrogen halide, for example, hydrogen chloride, is added to isoprene, it is thought that the following reaction takes place:

Isoprene hydrogen tertiary isoprene OH; H Cl H3C- CH:

Primary isoprene monohydrochloride however, there is some evidence that in the case of the chloride as distinguished from the bromide, that this rearrangement does not take place in large part, if at all.

Isoprene monohydrohalides may be prepared in the following manner:

Example 1 An isoprene fraction containing 70% by weight of isoprenewas obtained by the fractionation of condensate obtained in the manufacture of oil gas.

This fraction also contained some olefines boiling in the same range and possibly some piperylene and cyclopentadiene. Isoprene fractions of lower concentration may contain considerable quantities of these materials.

A quantity equivalent to approximately 476 parts by weight of this fraction was cooled to approximately C., whereupon a stream of dry hydrogen chloride was introduced intothe isoprene fraction over a period of hours, the temperature being maintained at approximately 0 C. throughout the entire time.

The mixture was then allowed to stand overnight and was then distilled.

That portion of the distillate boiling within the range of to 33 C. at mm. pressure, absolute, was collected as isoprene monohydrochloride.

That portion of the distillate boiling below 90 C. at atmospheric pressure and comprising for the most part unchanged isoprene, was retreated and distilled in the same manner. The distillate collected between 90 and 110 C. at atmospheric pressure was combined with the first distillate.

There was thus obtained a quantity of isoprene monohydrochloride equivalent to approximately 370 parts by weight. This fraction of isoprene monohydrochloride had the following physical properties:

Density (d 2o/4) =0.921a Refractive index (n 20/D) =1.43975 A quantity equivalent to approximately 260 parts by weight of hydrogen chloride was absorbed. This corresponds with the theoretical quantity required to add hydrogen chloride to one of the double bonds of the isoprene contained in the given quantity of starting material.

The preparation of isoprene monohydrohalide in the above manner may be carried out at any suitable temperature.

Temperatures between and 36 C. may be employed for the production of isoprene monohydrohalide in the liquid phase, isoprene boiling at the upper temperature limit indicated.

On the other hand, if desired, the reaction may be carried out in the vapor phase by employing temperatures above 36 C. although there are limiting factors such as the tendency of isoprene to form isoprene dihydrohalide, which may or may not be desired, or to polymerize at elevated temperatures in the presence of an acid catalyst.

In general, it is preferred to carry out the reaction in the liquid phase, while employing temperatures between --60 and 10 C.

If desired, halogenating catalysts may be employed to accelerate the addition of hydrogen halide to the isoprene molecule. Examples of halogenating catalysts are methyl alcohol and acetone.

The isoprene monohydrohalide thus obtained, namely the distillate boiling between C. and 110 C. at atmospheric pressure or, if desired, the crude reaction product prior to distillation, or any fraction thereof, whether narrower or wider than the above fraction, may be employed in the preparation of isoprene butyrate, although a fairly pure material is generally preferred.

The desired isoprene butyrate may be prepared (1) by converting the isoprene monohydrohalide into isoprene alcohol which is then reacted with the corresponding butyric acid, or its anhydride, or its acid halide, or (2) by reacting a metal derivative of isoprene alcohol, such as the sodium derivative (1. e., the alcoholate) with the selected butyric acid or its anhydride, or its acid halide, or (3) by reacting isoprene monohydrohalide directly such as with a metal butyrate of which potassium n-butyrate is an example. Mixtures of the isoprene butyrates may be prepared by using mixtures of the butyric acids, their anhydrides, or their acid halides, or combinations of the foregoing. The butyrates thus obtained may be separated, if desired, such as by distillation.

The conversion of isoprene monohydrohalide into isoprene alcohol may be effected in any desired manner, for example, the isoprene monohydrohalide may be hydrolyzed with aqueous alkaline solutions such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, calcium hydroxide, and similar reagents. In general, the use of mild alkalis such as sodium carbonate at moderate temperatures such as, for example, between 30 and C. and at moderate pressures such as, for example, between 1 to 2 atmospheres is preferred.

If desired, hydrolysis may be effected in the presence of a suitable solvent, such as for example toluene.

Upon hydrolysis of the halide, it is believed that a molecular rearrangement takes place as follows:

CH: H Cl OH: H t t t t CHx- Hz+H10 v CHr- 'C=CH2+HCI Isoprene monowater isoprene hydrogen hydrochloride alcohol chloride provided the rearrangement of tertiary isoprene monohydrochloride to primary monohydrochloride actually takes place. If not, then this step comprises the hydrolysis of the tertiary form.

The isoprene alcohol obtained in this manner may be refined by fractionation or otherwise, or if desired, the alcohol may be directly employed in the preparation of esters without refining. However, the former is frequently preferred.

Isoprene alcohol may be reacted with the butyric acid or its anhydride, or its acid halide, by combining the reactants, preferably with the such as benzene, particularly when employing the refluxing method.

Since the reaction forms water, there is produced a ternary mixture consisting of isoprene alcohol, benzene and water. The water formed may be removed during the esteriflcation' reaction if desired. This may be accomplished, for instance, by permitting the reflux condensate to collect and stratify in a separate receptacle, whereupon the water layer is continuously removed and the remainder of the condensate is returned to the reaction zone.

On the other hand, the water may be removed, after the reaction has become completed, among other ways, by separating the liquid layers,

whereupon the solvent and unreacted alcohol may be removed from the reaction product by distillation or otherwise.

. Unreacted butyric acid present in the reaction product may be neutralized by an alkali or alkaline solution, if desired, suchas sodium bicarbonate, preferably before the removal of solvent and unreacted alcohol. On the other hand,

the unreacted butyric acid may be separated from the other constituents by distillation.

The preparation of isoprene alcohol and its reaction with isobutyric acid is illustratedin the following example.

Example 2 Boiling point, 95-100 c. at 760 mm. Density (a 20/4) =0.8255 Refractive index (11. 20 /D) =1.41446 Approximately 344 parts by weight of the isoprene alcohol thus prepared was added to a mixture of 1'76 parts of isobutyric acid and 400 parts of benzene. This mixture was treated-with 19 parts of anhydrous hydrogen chloride and refluxed for a period of approximately 12 hours after which the water of reaction, amounting to approximately 36 parts, was removed. The benzene and excess isoprene alcohol was removed by distillation, after which the residue was neutralized with a sodium bicarbonate solution to remove hydrogen chloride and any unreacted isobutyric acid.

The residue was fractionated at a pressure of 10 mm. of mercury, absolute, to obtain a waterwhite liquid possessing an exceptionally pleasant fruity odor.

The quantity secured was approximately 70 parts by weight.

This particular isoprene isobutyrate fraction was found to have the following physical properties:

Boiling point 585-63 C. at 10 mm. absolute Density (d 20/4 =0.8647 Refractive index (n 20/D)=1.43610 If desired, other esterification catalysts, such as sulfuric acid, phosphoric acid, and the like, may be employed, or the reaction may be carried out in the absence of a catalyst.

As pointed out above isoprene isobutyrate may also be prepared by reacting a metal salt of isobutyric acid with isoprene monohydrohalide. Refluxing the materials over a period of several hours has been found to be particularly effective. The presence of isobutyric acid facilitates the reaction.

After the reaction is complete, residual isobutyric acid, if any, may be neutralized, if desired, after which the ester formed may be recovered in any suitable manner, for instance, by extraction and the ester may be separated in any suitable manner, such as by distillation whereupon the ester may be further fractionated, ,if desired. Other separating and/or refining methods, as for example, the direct fractionation of the crude reaction mixture, may be used if desired.

The reaction between a metal salt of isobutyric acidand an isoprene monohydrohalide is illustrated in the following example.

Example 3 A mixture of 200 parts by weight of isoprene hydrochloride, 250 parts by weight of potassium isobutyrate, and 200 parts by weight of isobutyric' acid were refluxed for a period of approximately three hours. The reaction mixture was then cooled, poured into an equal volume of water, and neutralized with an alkaline solution such as sodium bicarbonate.

The isoprene isobutyrate thus formed was extracted with diethyl ether; the ether removed by distillation, and the residue fractionated.

. There was thus obtained approximately 124.

parts by weight of an isoprene isobutyrate fraction having the following physical properties:

Boiling point 61-65 C. at 11 mm., absolute Density (d 20/4) =0.8950 Refractive index (n 20/D)=1.4294

The product has a very pleasant odor, entirely free from the disagreeable odor of isobutyric acid.

The preparation of isoprene n-butyrate from n-butyric acid and isoprene alcohol is illustrated by the following example.

Example 4 into water and neutralized by the addition of sodium bicarbonate.

The ester was then extracted with diethyl ether. The ether extract was distilled at atmospheric pressure, after which the residue was fractionated under reduced pressure.

A total of 69.8 grams of the n-butyl ester of isoprene alcohol was obtained; It is a colorless limpid liquid with a pleasant ester odor, and having the following physical properties.

Boiling point=105-110 C. at 50 mm. Density (d 20/4)=0.9047 Refractive index (n 20/D) =1.43687 The preparation of isoprene n-butyrate by the reaction of a metal salt of n-butyric acid with an isoprene monohydrohalide is illustrated in the following example.

Example 5 A 190 gram portion (1.5 mols) of freshly pretrate was distilled under reduced pressure to remove the butyric acid, after which the crude ester was treated with a 10% solution of sodium bicarbonate, extracted with ether, and dried over anhydrous sodium sulfate.

After the removal of the ether on a hot water bath, the residue was distilled under reduced pressure. Approximately 111 grams of isoprene nbutyrate was secured, having the following physical properties.

Boiling point= C. at 3 mm., absolute Density ((1 20/4) =0.8978 Refractive index (n 20/D)=1.43301 Other metal derivatives of n-butyric acid or isobutyric acid, such as the sodium, calcium, iron, lead, or other metal salts, may be substituted for the potassium salts given in the foregoing ex- I amples. The reaction may be carried out in the presence or absence of the free acid or anhydride, and in the presence or absence of a solvent such as benzene. The reaction may be carried out at any suitable temperature, such as the boiling point of the mixture, and may be carried out at any suitable pressure, such as atmospheric, subatmospheric, or superatmospheric pressures.

The properties of isoprene n-butyrate and isoprene isobutyrate make them excellent solvents or plasticizers for paints, lacquers, varnishes, enamels, and similar coating compositions. They are also particularly valuable as intermediates in chemical synthesis. Their unsaturated nature makes them convenient compounds for introducing additional constituents, thereby making possible the production of a wide variety of isoprene and isoprene butyrate derivatives. The exceptionally pleasant odor of these materials recommends them for many uses to which materials of this character are put, such as in perfumes, soaps, pharmaceutical preparations, et

cetera.

The use of these derivatives as lacquer solvents is illustrated by the following examples.

Example 6 A base mixture of the following components:

Parts Ester gum 2.5 Nitro cellulose 5 Dibutyl phthalate 2.5

was thoroughly incorporated in 40 part of the following solvent mixture:

Parts Amyl alcohol 10 Isopropyl acetate 1 3 Anhydrous ethyl alcohol 3 Toluol 34 Saturated hydrocarbon fraction obtained in the pyrolysis of petroleum oil, (B. P. -120" 0.) known commercially as troluol 20 Isoprene n-butyrate 20 Example 7 A base mixture of the following components:

Parts Cellulose acetate 6.5 N-butyl ester of 3-methyl-A4-tetra-hydrophthalic anhydride 0.5

was thoroughly incorporated in 93 parts of the following solvent mixture:

, Parts Acetone 50 Ethylene glycol monoethyl ether 20 Toluene 15 Isoprene isobutyrate 20 A clear lacquer was obtained which was applied to the surface of metallic panels and permitted to dry overnight. A colorless, flexible, adherent coating was obtained.

While the invention has been described more particularly in connection with n-butyric acid and isobutyric acid, in its broadest phases, it also includes substituted n-butyric acids and substituted isobutyric acids.

The invention also comprehends the preparation of mixed esters, such as by the reaction of a mixture of n-butyric and isobutyric acids with isoprene alcohol, or otherwise. It also comprehends the production of mixed esters by the reaction of a mixture of two or more acids, of which at least one is normal butyric acid or isobutyric acid with isoprene alcohol, or otherwise.

Therefore, in the claims, the term butyric compound embraces normal butyric acid and isobutyric acid, substituted normal butyric acid and isobutyric acid, their salts, anhydrides, and acid halides. Also in the claims, the term n-butyric acid or isobutyric acid includes the anhydride, or mixtures of the acid and anhydride. The term hydrogen halide embraces hydrogen chloride, bromide, iodide and fluoride. The term isoprene hydrohalide" embraces the isoprene derivatives of these four hydrogen halides. The term isoprene" includes pure isoprene, technical or commercial grades thereof when produced, iso; prene solutions, and hydrocarbon fractions containing any quantity of isoprene regardless of source. The term isoprene derivative is intended toembrace the hydroxyl derivative of isoprene, the metal derivatives of said hydroiwl derivative (i. e., the alcoholate) and the monohydrohalides of isoprene. The term metal butyrate includes potassium, sodium, calcium, iron, lead, and other such salts of normal butyric acid or isobutyric acid. Additionally, the term esterification catalyst includes such compounds as sulfuric acid, phosphoric acid, anhydrous hydrogen chloride, and the like.

While reagents and procedures of a particular nature have been specifically described, it is to be understood that these are by way of illustration. Therefore, changes, omissions, additions, substitutions and/ or modifications might be made within the scope of the claims without departing from the spirit of the invention which is intended to be limited only as required by prior art.

I claim:

1. A butyric ester of Z-methyl-Z-hydroxy butane-3 corresponding to the formula isoprene, with a compound capable of yielding a butyric acid radical.

5. A process for preparing a butyric ester of 2-methyl-2-hydroxy butene-3 comprising reacting one of a group consisting of 2-methyl-2- hydroxy butane-3 derivedfrom light oil isoprene and a metal derivative of said 2-methyl-2-hydroxy butene-3 with one of a group consisting of a butyric acid and an acid halide of a butyric acid.

6. The process of preparing a butyric ester of 2-methyl-2-hydroxy butene-3 which comprises contacting a light oil isoprene fraction with a hydrogen halide to form a methyl halobutene, and reacting said methyl halobutene with a metal butyrate. I

7. In the process of claim 5, the step of effecting esterification in the presence of an esteri-.

flcation catalyst.

8. In the process of claim 6, the step of effecting esterification in the presence of a solvent.

9. In the process of claim 5, the step of continuously removing water during the esterification reaction. I

10. In the process of claim 6, the step of con- .acting the isoprene fraction with a halogen halide in the presence of a halogenating catalyst.

11. In the process of claim 6, the step of effecting esterification in the presence of a butyric acid.

12. The process of preparing a butyric ester of 2-methyl-2-hydroxy butane-3 which comprises contacting a light oil isoprene fraction with a hydrogen halide to form a methyl halobutene, hydrolyzing said methyl halobutene to form a methyl hydroxybutene, and reacting said methyl hydroxybutene with a compound capable of yielding a butyric acid radical.

' FRANK J. SODAY. 

